Here is one for you Steve.
When reviewing the SLs PSA pop report totals there is some interesting data showing up.
I broke the 48 SLs up into two groups, the 34 printed with OM/Pied/Hindu & the 14 printed with OM/Piedmont.
The 34 group has an average ratio of
.76 Piedmonts per OM printed (51%-103%)
The 14 group has an average ratio of
1.6 Piedmonts per OM printed (140%-221%)
Those
14 show up on average more than double with Piedmonts than the other 34 group. Based on the pop numbers it appears that those 14 SLs were printed at one point (or always) separately than the 34.